All the enzymes are proteins and they are produced by the living cells. They act as biological catalysts. Enzymes catalyse and enhance the rate of biochemical reactions occuring in various vital processes like breathing, digestion, pumping of heart, formation of body tissues, contraction of muscles, transport of ions across the plasma membranes etc.So without enzymes there is no life. They are inactive at OoC and destroyed by moist heat at 100oC.
The term enzyme was first used by Kuhne (1878) to designate these ‘biological catalysts’. Sumner and My Back (1950) have defined the enzymes as “Simple or combined proteins acting as specific catalysts”. They affect the life of an organism to such an extent that life has aptly called as an orderly function of enzymes.
The substances on which the enzymes act are called as “Substrates”. Enzymes are highly specific in their action (i.e) an enzyme can act on a single or a small group of closely related substrates. During catalytic action, the enzymes do not undergo any permanent modification and regenerated at the end of the reaction. The general enzyme catalysed reaction takes place as per the equations
E - Enzyme; S = Substrate; ES - Enzyme-Substrate complex;
P = product. ES complex is an unstable and highly energised complex.
α-amylase acts on starch and produce maltose units. In this reaction a-amylase is the enzyme, starch is the substrate and maltose is the product.
Most of the enzymes, synthesised by a living cell, function within that cell and hence are called as endo enzymes or intra cellular enzymes. Some enzymes are liberated from the living cells after synthesis, secreted to the environment and function in extra cellular regions. These enzymes are called as exoenzymes or extra cellular enzymes.